(a) Field of the Invention
This invention relates to a method of potting an electronic component, and also to potted electronic components per se.
This invention is especially suitable for use in connection with the manufacture of reed relays, though it may be used for the manufacture of a variety of other electronic and electrical components. In the following, reference will mostly be made to reed relays, but it will be appreciated that the invention is not limited to such electronic components.
(b) Description of the Prior Art
Electronic components for use in the construction of electronic circuits frequently are "potted"--that is to say, encapsulated within a polymerised synthetic resin material. When potted in this way, a component is hermetically sealed from the ambient and also is protected against physical damage. In addition, depending upon the resinous potting compound employed, potting may be particularly advantageous for components subjected to high voltages, to minimise the risk of insulation breakdown.
A minature reed relay usually consists of the contact elements contained within an envelope (known as the `insert`) and an operating coil within the core of which is positioned the insert. It is a common practice to encapsulate the insert together with its operating coil, so as to hold the reed relay insert and its operating coil in the required relative disposition, as well as to protect the relatively delicate coil and relay insert against mechanical damage. However, potting a reed relay inevitably increases the bulk of the relay, and this can lead to problems when it is desired to pack a number of such relays into a relatively small space on a printed circuit board.
When a plurality of reed relays are arranged very close to one another on a printed circuit board, problems may arise due to magnetic interaction between the coils of adjacent relays. Thus, though the operating characteristics of a complete reed relay may be determined for that relay in isolation, the characteristics may be significantly altered--and particularly the operating voltage of the relay--when a number of relays are packed closely together.
In an attempt to overcome the above-stated problem, it is known to enclose a reed relay within an envelope or casing which is made of a metal having a high magnetic permeability, so as to magnetically isolate the relay within the casing. When the bulk of a completed relay is not important, magnetic isolation can easily be achieved in this way, but it has proved to be extremely difficult to effectively isolate a reed relay when the overall size of the relay is to be reduced to the smallest possible dimensions to permit very high packing densities for such relays on a printed circuit board.
Conventionally, casings for magnetic screening are made either from soft iron or .mu.-metal using a deep drawing technique or--in the case of relatively large components--a conventional case-manufacturing technique. However, especially when using .mu.-metal, experience has shown that it is very difficult to reduce the wall thickness of a deep drawn casing to below 0.5 mm--and inevitably this therefore considerably increases the overall size of an electronic component potted within such a casing.